In a list of more than 200 bay area neighborhoods compiled by Zillow.com, three expensive enclaves in and around Pinellas County's second city took the biggest price pounding.

The online real estate service reported that, overall, Tampa Bay area home values declined 19.8 percent in the first three months of this year compared with the same period in 2008. But in Clearwater Beach, the decline was 29.5 percent. Nearby Sand Key suffered a drop of 28 percent. Down the road in Belleair Beach, values tanked 26 percent.

Realtors who work the Clearwater market aren't surprised. The area's condo market rose disproportionately during the boom on the backs of pricey bayfront properties like Sand Pearl Resort and Mandalay Beach Club. The crash has sent prices spiraling back to earth.

Second-home sales have collapsed across the nation as buyers defer such purchases or are denied by their banks. Banks have confiscated hundreds of properties, which can sell for half of what they once did.

"What we're seeing is two markets — the foreclosure market and the other market," said Joan Leeds, an agent with Prudential Tropical Realty. "Prices on the beaches went up so much higher, so much more quickly, with all the speculators out there.''

Not all Tampa Bay area waterfront is hurting the same way. Housing values in St. Pete Beach were down 18.6 percent year over year. Homes depreciated 19.1 percent in Harbour Island in Tampa. The drop in southeast Hillsborough County's Apollo Beach community was 15.5 percent.

Clearwater Beach, Sand Key and Belleair Beach are noteworthy for being among the most expensive neighborhoods in the region.

The average home value in Pinellas, Pasco, Hillsborough and Hernando counties was $136,797, Zillow said. By contrast, Clearwater Beach came in at $287,318, Belleair Beach at $346,884 and Sand Key at $335,496.

Local Realtors said even wealthier beach lovers are postponing purchases in anticipation of further price declines. Zillow agrees, and suggests we won't reach a price bottom until 2010.

In fact, 21 percent of local home buyers who took out mortgages in the first part of 2009 already have negative equity in their homes. Nearly half the homes bought with mortgages last year are underwater.

That's partly because loans backed by the Federal Housing Administration generally require only 3.5 percent down payments. Even a relatively minor devaluation can wipe out that investment.

"Additional information we have this quarter on 'shadow inventory,' with one-third of homeowners indicating they would like to put their home on the market if conditions improve, confirms our earlier fears that a bottom in home values could be quite protracted," said Stan Humphries, Zillow vice president of data and analytics.

"By our calculations, this could translate into as many as 20 million homes that could seep into the market as prices stabilize, maintaining a constant stream of supply that far outpaces demand, thus keeping prices flat," he said.